This invention relates to an earthwork machine control device which permits an earth-work machine such as a power shovel to readily conduct straight excavation.
If the position of a hydraulic power shovel as shown in FIG. 1 is expressed by x-y coordinates as shown in FIG. 2, the position (x, y) of the top of the earthwork machine (the sharp edge D of the bucket 3) is as indicated by the following equations (1) and (2) as well known in the art: EQU x=L.sub.1 .multidot.sin .alpha.+L.sub.2 .multidot.sin (.alpha.+.beta.)+L.sub.3 .multidot.sin (.alpha.+.beta.+.gamma.) (1) EQU y=L.sub.1 .multidot.cos .alpha.+L.sub.2 .multidot.cos (.alpha.+.beta.)+L.sub.3 .multidot.cos (.alpha.+.beta.+.gamma.) (2)
where
original point O: the boom 1 pivoting fulcrum PA1 point B: the arm 2 pivoting fulcrum PA1 point C: the bucket 3 pivoting fulcrum PA1 L.sub.1 : the length between the points O and B PA1 L.sub.2 : the length between the points B and C PA1 L.sub.3 : the length between the points C and D PA1 .alpha.: the angle between the y-axis and the segment OB PA1 .beta.: the angle between the segments OB and BC PA1 .gamma.: the angle between the segments BC and CD that is, the angle between an arm and a top opening plane of a bucket
In this connection, the x-axis is the line of intersection of a plane including the points O, B, C and D and a plane including the boom fulcrum O and in parallel with the ground surface on which the vehicle is positioned; and the y-axis is a straight line passing through the boom fulcrum O and perpendicular to the ground surface. The angle .alpha. can be varied by telescoping the boom cylinder 4. Similarly, the angles .beta. and .gamma. can be varied by the arm cylinder 5 and the bucket cylinder 6, respectively.
On the other hand, for straight excavation (the excavation locus being straight) it is necessary to straightly move the sharp edge D, i.e. the position (x, y) of the sharp edge D must meet the following equation (3): EQU y=M.multidot.x+N (3)
where M and N are optional constants.
Heretofore, the following system is employed according to the above-described principle: First, conditions such as excavation surface inclination (corresponding to M in the equation (3)), excavation depth (corresponding to N in the equation (3)), bucket excavation angle (corresponding to (.alpha.+.beta.+.gamma.) in the equations (1) and (2)) and excavation speed are provided by means of an operating board or levers. According to a principle similar to that of the equations (1) through (3), the amounts of operation (corresponding to the angles .alpha., .beta. and .gamma. or the angular velocities .alpha., .beta. and .gamma.) of the hydraulic cylinders 4, 5 and 6 necessary for straight excavation are calculated from these conditions and the angles .alpha., .beta. and .gamma. outputted by detectors. Then, according to the calculation results, the boom angle .alpha., arm angle .beta. and bucket angle .gamma. are controlled. This calculation can be achieved according to various systems.
However, the system in which the amounts of operation of the cylinders 4, 5 and 6 are calculated from the conditions provided by the control board or the like and the resultant values are employed as input signals to control the operations of the relevant parts, is disadvantageous in the following points: It is necessary to provide a calculation unit or units for calculating the amounts of operation of the cylinders 4, 5 and 6 and control units for controling the operations of the cylinder 4, 5 and 6 according to the calculation results thereof. Accordingly, the system itself is expensive. In addition, if any one of the control units provides control error by being affected by external disturbance or the like, then the excavation locus will not be straight.
Hydraulic circuits for driving the hydraulic cylinders 4, 5 and 6 are, in general, provided with relief valves for security. If any one of the hydraulic cylinders is overloaded by the presence of an obstruction during the excavation, then its relief valve is opened so as to stop the hydraulic cylinder. In this case, the remaining hydraulic cylinders are operated as calculated, and therefore it becomes impossible to perform the aimed straight excavation.